A 200-fold inhibition in the titer of infectious vesicular stomatitis virus (VSV) was achieved in cultures of L-cells treated with 30 reference units/ml of interferon (IF); however virus particle production, as measured by VSV particle-associated RNA, nucleocapsid (N) protein, or transcriptase activity, was inhibited by a maximum of 10-fold by this concentration of Interferon. A significant reduction was seen in the glycoprotein (G) and matrix protein (M) content of VSV from interferon-treated cells. Electron-microscopic studies also support the deficiency of glycoprotein in VSV released from interferon or tunicamycin-treated cells. The incorporation of N-acetylglucosamine into glycolipids with the properties of dolichol derivatives is lower in membranes prepared from interferon-treated cells as compared to the untreated cells. These results suggest that interferon inhibits the glycosylation of a viral protein in this system.